Portsmouth Basin, Me. and N. H. lot 



from experimental evidence, only to be produced in the 

 wet way. Tims to the theory of fractional crystalli- 

 zation under gravitative control a necessary addition 

 would seem to be the influence of mineralizing solu- 

 tions in furthering changes in composition. It is entirely 

 probable that for a given locality either of these agencies 

 may have been chiefly responsible for a given rock type. 

 In the case of the Durham body, since it shows marked 

 contact effects, it would seem necessary to assign an 

 important role to the action of the volatile components 

 in producing the granite. 



The alkaline rocks offer a more complex problem. In 

 this case a biotite granite is succeeded by alkaline granite 

 which in turn is apparently followed by alkaline rocks 

 carrying less and less quartz but rich (10-13%) in such 

 elements as soda and potash. Here and there in these 

 alkaline rocks are found coarse pegmatitic phases in 

 which the crystals of feldspar measure up to 10 centi- 

 meters in length and the alkaline hornblende 5 to 6 centi- 

 meters. The development of soda — and potash — rich 

 minerals and the presence of pegmatitic phases are both 

 interpreted as indicating that mineralizers were active 

 agents in producing these peculiar rock types. There 

 are, however, other factors, which must be reckoned with. 

 The experimental work of Bowen indicates that frac- 

 tional crystallization under gravitative control may 

 largely influence the process of differentiation. The 

 contacts of the subjacent bodies against the sedimen- 

 taries certainly indicate that magmatic stoping was one 

 of the means of emplacement. The figures dealing with 

 specific gravities appear to show that much of the stoped 

 material would sink. With stoping a factor of emplace- 

 ment, then the assimilation of the stoped blocks would 

 seem necessary since the contact actions show that the 

 process actually takes place. Such stoped and assimi- 

 lated material ought to make itself felt as the process of 

 differentiation continues. Both of these aforementioned 

 processes have evidently exerted a control upon the 

 differentiates, but to the writer it seems that their effects 

 were furthered by volatile components which not only 

 aided assimilation but also were active in producing the 

 upward transfer of the alkaline constituents so necessary 

 in producing the alkaline rock types. 



